Biocompatible AIE material from natural resources: Chitosan and its multifunctional applications.

New sources of AIE materials with good water solubility, biocompatibility, degradability, and mass production are urgently needed. Here, we found that chitosan, a very abundant polysaccharide in nature, has fluorescence emission in both solid and solution states with AIE effect, and explored its multifunctional applications. Chitosan can emit a variety of colors from blue to red at different excitation wavelengths with excellent multicolor imaging capabilities at the cellular level. Utilizing the cationic and antibacterial properties of chitosan, the quantification of bacteria can be achieved through the AIE effect. Concurrently, it can be used as fluorescent probes for multi-channel bacterial imaging via lighting-up bacteria. Furthermore, the chitosan solution exhibits a sensitive quenching response to Fe, which can be used as a biosensor for detecting the concentration of Fe. These interesting results indicate that chitosan will have broad application prospects as a new class of AIE material.